1. Field of the Invention
This invention relates to inhibitors, compositions, and processes for deoxidizing and cleaning surfaces of aluminum and its alloys that contain at least 55% by weight of aluminum (all such alloys being hereinafter to be understood as encompassed within the scope of the term "aluminum" unless the context requires otherwise), while minimizing the etching of titanium. "Deoxidizing" is to be understood herein as the removal from the surface of metals of oxide films and other adherent inorganic materials that would reduce adhesion to subsequently applied protective coatings such as conversion coatings and/or paints and the like, and "cleaning" means removal of all other foreign materials, especially organic soils and poorly adherent inorganic substances such as metal dust and the like, that would reduce adhesion to such subsequently applied protective coatings.
2. Statement of Related Art
With most deoxidizing agents, especially acidic aqueous liquid compositions with substantial hexavalent chromium and/or free fluoride ion contents, such compositions being probably the most effective chemical classes of cleaners and deoxidizers for aluminum now known, there is a perceptible but controlled etching or dissolution of the aluminum, from its surface inward, while the deoxidizing agent is in contact with it. In the aerospace industry in particular, such deoxidizing is considered a necessity for achieving adequate corrosion resistance for many uses of aluminum. The aluminum parts being deoxidized are conventionally held by racks or other structures of titanium during the deoxidizing process, and etching of these titanium structures during the deoxidizing of aluminum is very disadvantageous, as it decreases the lifetime of the titanium structures and would necessitate frequent replacement of these expensive items.
Hexavalent chromium-containing deoxidizing liquid compositions for the types of aluminum alloys most commonly used in aerospace have low etch rates for titanium. However, the pollution problems associated with hexavalent chromium have motivated efforts to eliminate or reduce its use as much as possible. Previously developed chromium-free deoxidizers for aluminum, however, have had unsatisfactorily high etch rates on titanium and/or have required an additional process step compared with conventional deoxidizing of aluminum with the use of hexavalent chromium containing deoxidizing liquid compositions, thereby making them unacceptable to most commercial users.